Fehmarn Link Contractors (FLC) have cast a full-scale model of a tunnel segment. The purpose of the test casting was to get confirmation of the composition of the concrete mix, the work processes at the production lines, and the ideal temperature when liquid concrete has to be pumped over long distances. And to find out, it was necessary to drill a good amount of holes in the pre-cast concrete segment, to get drill cores out for further analysis.
First analyses are over
Now the first analysis work is over, and according to the technical director from Femern A/S, Jens Ole Kaslund, valuable knowledge has come out of both trial casting and the core analyses:
– As expected, the first full-scale test casting provided valuable experiences that can optimize the process and train the workers. The purpose was to test our concrete mix, the moulds, the rails and the pistons that push the elements forward, and the sequence in which the tasks are carried out. All the elements we will use in the factory, such as water stoppers and end frames, were included in the trial casting. During and after the casting, we kept an eye on the technical challenges we faced during construction in order to be able to improve the processes if necessary, says Jens Ole Kaslund.
79 standard elements and 10 special
A total of 79 standard tunnel elements are to be manufactured, each 217 meters long and 42 meters wide. Each element consists of nine segments of just over 24 metres. Each of the 79 elements weighs over 73,000 tons.
In addition to the standard elements, the element factory in Rødbyhavn will also produce 10 special elements, each 39 meters in length and 45 meters in width. The special elements must also have a “basement floor” for the tunnel’s technical installations, emergency exits and lifts. The extra width of the special elements also needs to be useable by emergency and work vehicles.
Six production lines in operation all day and all night
When work on the element factory begins at the end of 2022, work must be ongoing 24 hours a day, 365 days a year. Six production lines must work when the element factory reaches its peak load. Therefore, it is crucial that no “surprises” arise. It was precisely the purpose of building the full-scale model, to become aware of any problems concerning technology, methods and processes before they appear.
Therefore, a test casting will probably have to be carried out later in the autumn, where the experiences from the first one will be incorporated. And significant and valuable experience has already been gained:
Handover between the concrete crews
– After the casting, we have, for example, made a series of boreholes in the finished test element to study where the concrete has hardened. Overall, our test casting shows that the production method works well and that the method can be scaled up. One of the lessons we have learned is to ensure a uniform temperature, not only in the casting halls but also in the up to 400-meter-long pipes the concrete must be pumped through if a homogeneous concrete mix is to be ensured. We have also become aware of the importance of ensuring a good and detailed handover between the different concrete crews. When we do the second trial casting this autumn, we will take all those lessons with us, explains Jens Ole Kaslund from Femern A/S to FemernReport.
